On Mon, Apr 7, 2025 at 08:31 PM, <andrey@...> wrote:
I used a lab PSU at 7V initially; QMX draws ~150 mA right away - not proper.
150-200mA is fine for QMX without firmware, in firmware update mode presenting USB drive.? Assuming the current draw happened after you pressed the power-on button.
But at the same it did power-up and display lights up.
If display light comes on without firmware installed, there is a problem.? It? uses 5V power supply, which is only started by firmware.? Are you sure this happened with no firmware installed?
So I tried USB connection and was able to flash the firmware successfully.
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- it self-turns on;
- MCU probably thinks it is underpowered: as soon as it boots and displays normal view, it shows "Shut down!" and cycles;
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If it 'self? turns on', and then does 'shutdown', without you pressing the power-on button, it likely means the power-on signal is stuck in the 'on' position.?? That would cause it to self-turn on, and the MCU, after booting, would see the power-on/off button asserted, and do its shutdown sequence.
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So the first thing to do is verify the power-on button from the encoder, and all of the connections of the PWR_ON signal to the main board (see the schematics, it goes through pin 1 of the 8-pin).? It is likely that the signal is shorted to ground (or to another low signal, like the adjacent PWM_5V pin) somewhere along that path.?
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This could also cause the display backlight to flash, since the MCU will start up the 5V, but then quickly shut it down again because it thinks you are pressing the power on/off button to shut it down.
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First solve that issue, and keep using the 7V supply, and then we can investigate the high current draw if it isn't resolved.
Stan KC7XE
